Stabilized polyoxymethylene molding compositions containing a mixture of an alkaline earth metal salt and an ester of(alkylhydroxyphenyl)-carboxylic acids with a polyol

ABSTRACT

THE STABILIZATION OF POLYOXYMETHYLENES AGAINST OXIDATION AND THERMAL DECOMPOSITION IS CARRIED OUT BY ADDING A COMBINATION OF ALKALINE EARTH METAL COMPOUNDS AND ESTERS OF (ALKYL-HYDROXYPHENYL)-CARBOXYLIC ACIDS WITH POLYOLS. MOLDING COMPOSITIONS MADE FROM POLYOXYMETHYLENES SO STABILIZED MAY BE THERMOPLASTICALLY PROCESSED: THEY ARE SUITABLE FOR THE MANUFACTURE OF SEMI-FINISHED AND FINISHED GOODS.

United States Patent 3,743,614 STABILIZED POLYOXYMETHYLENE MOLDING COMPOSITIONS CONTAINING A MIXTURE OF AN ALKALINE EARTH METAL SALT AND AN ESTER OF (ALKYLHYDROXYPHENYL)-CARBOX- YLIC ACIDS WITH A POLYOL Ernst Wolters, Frankfurt am Main, and Gunther Roos, Kelkheim, Taunus, Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany No Drawing. Filed Aug. 31, 1971, Ser. No. 176,693 Claims priority, application Germany, Sept. 2, 1970, P 20 43 498.4 Int. Cl. C08g 51/56 US. Cl. 260-18 R 6 Claims ABSTRACT OF THE DISCLOSURE The stabilization of polyoxymethylenes against oxidation and thermal decomposition is carried out by adding a combination of alkaline earth metal compounds and esters of (alkyl-hydroxyphenyl)-carboxylic acids with polyols. Molding compositions made from polyoxymethylenes so stabilized may be thermoplastically processed; they are suitable for the manufacture of semi-finished and finished goods.

The present invention relates to stabilized molding compositions on the basis of polyoxymethylenes.

It is known that polyoxymethylenes, i.e. homoor copolymers of formaldehyde or of cyclic oligomers of formaldehyde, for examplev trioxan, can be stabilized against the influence of heat and oxygen by addition of stabilizers.

As stabilizers, for example phenols, amines, amides, amidines, hydrazines, ureas, thioureas and polyamides are used. The stabilizing effect of these substances is based on their capability to absorb the aldehydes and their by-products which are formed by thermal chain cleavage, to block the active centers in the. polymer and, thus, to prevent depolymerization.

The efliciency of the above substances varies considerably. The derivatives of hydrazine, urea and thiourea have only a slight stabilizing effect against heat .and oxygen. The amine stabilizers, however, though being excellent antioxidants, cause a brown to black discolora tion of the polyoxymethylenes. Part of the known phenolic stabilizers also cause discolorations, and other stabilizers easily diifuse out of the polymer or can be dissolved out, in which case the stability of the products stabilized by these substances deteriorates under theaction of heat and/or upon contact with solvents.

It has now been found that'polyoxymethylenes can be excellently stabilized against oxidation and thermal degradation by using acombination of alkaline earth metal compounds and esters of (alkyl-hydroxyphenyl)- carboxylic acids with polyols.

It has already been proposed to use different hydroxy- Q phenyl-alkanoic acid compounds as stabilizers for or ganic substances, especially for poly-olefins (cf. German Pats. Nos. 1,163,017 and 1,201,349, German Auslegeschrift No. 1,286,041, Belgian Pat. No. 636,254 and Netherlands patent application No. 6808946). It is also known that hydroxyphenyl-alkanoic acid compounds can be used for the stabilization of polyoxymethylenes (cf. French Pat. No. 1,489,414).

Surprisingly, certain particular hydroxyphenyl-carboxylic acid esters in combination with alkaline earth metal compounds show a substantially more favourable sta bilization efiiciency in polyoxymethylenes than the known hydroxyphenyl-alkanoic acid esters, which is due to a strong synergistic efiect of the compounds.

The present invention provides stabilized molding compositions on the basis of polyoxymethylenes containing (1) from 0.05 to 4, preferably from 0.1 to 2% by weight, calculated on the polyoxymethylene, of compounds of the formula in which R represents an alkyl radical having from 1 to 6, preferably from 1 to 4 carbon atoms, R is a hydrogen atom or an alkyl radical having from 1 to 6, preferably from 1 to 4 carbon atoms, A stands for a bito hexavalent, preferably bito tetravalent, straightchain or branched aliphatic hydrocarbon radical having from 1 to 12, preferably from 1 to 6 carbon atoms, m is zero or an integer of from 1 to 6, preferably zero, 1 or 2, and 11 corresponds to the valence of A, and

(2) from 0.01 to 3, preferably from 0.1 to 2% by weight, calculated on the polyoxymethylene, of alkaline earth metal salts of carboxylic acids having from 10 to 20, preferably from 12 to 18 carbon atoms, and/ or alkaline earth metal hydroxides.

The stabilizer combination used according to the invention neither can be dissolved out by usual solvents, nor diffuse out of the polyoxymethylene under thermal load, so that the molding compositions of the invention are especially suitable for use at high temperatures or in contact with solvents. The stabilizers used are colorless and do not or only insignificantly discolor the polyoxymethylenes even under a prolonged influence of heat, light or alkaline media.

Esters of araliphatic or aromatic carboxylic acids substituted in the nucleus, suitable for use as component l) of the stabilizer combination are for example especially esters of araliphatic or aromatic monocarboxylic acids having from 7 to 13, preferably from 7 to 9 carbon atoms, the aromatic nucleus of which, in 3- or 3- and i-position, is substituted by an aliphatic alkyl radical having from 1 to 4 carbon atoms and of straight-chain or branched monoto tetrahydric alcohols, for example esters of w-(3-tert.-butyl 4 hydroxyphenyl)-pentanoic acid, of fi-(3-methyl 5 tert.-butyl 4 hydroxyphenyl)- propionic acid, of 3,5-di-tert.-butyl-4-hydroxy-benzoic acid, of 3,5-di-tert.-butyl-4-hydroxy-phenyl acetic acid, of 5-(3,5-di-tert.-butyl-4hydroxyphenyl)-propionic acid or of (3,5-di-isopropyl-4-hydroxyphenyl)-acetic acid with ethylene glycol, propanediol-(l,2), propanediol-(1,3), butanediol-(1,4) hexanediol-( 1,6) decanediol-(1,l0) 1,1,1-trimethylol-ethane or pentaerythritol.

As alkaline earth metal compounds, the hydroxides of magnesium, calcium, barium and strontium or the salts .of these metals with saturated or unsaturated carboxylic acids having from 10 to 20, preferably from 12 to 18 carbon atoms, are especially suitable. The carboxylic acids may also be substituted by OH groups. Especially advantageous are the calcium salts of lauric acid, stearic acid and ricinoleic acid.

If necessary, the molding compositions according to the present invention may contain further stabilizers, for example known light stabilizers, such as derivatives of benzophenone, acetophenone or triazine. Other known additives, such as dyestuffs, pigments or fillers may also be '1 dissolved in a suitable solvent, for example methanol, acetone or methylene chloride, and applied to the polymer, while stirring. Subsequently, the solvent is evaporated.

Polyoxymethylenes which may be stabilized in accordance with the present invention, are homopolymers of formaldehyde or of cyclic oligomers of formaldehyde, for

The stability of the polyoxymethylenes towards heat and oxidation is examined by determining the loss of weight of a granular sample after 45 minutes or 120 minutes at 230 C. in air. In order to determine the color value and the color stability, round color samples in the example, trioxan, the terminal hydroxyl groups of which form of flats are fabricated from the individual testing are blocked by esterification or etherification, and copolygranules, the flats having a thickness of 2.5 millimeters mers of formaldehyde or of cyclic oligomers of formaldeand a diameter of 4.5 centimetres and their yellow value hyde, preferably trioxan, which contain oxyalkylene is measured in a differential colorimeter. (Colormaster groups with at least two, preferably from two to four adequipment of Manufacturing, Engineering and Equipjacent carbon atoms in the main valence chain. The proment Corporation, Hatboro, Pa.) before and after heatportion of comonomers in the copolymers is of from 0.1 ing for 30 minutes at 230 C. in a closed mold. to 50% by Weight, preferably from 0.1 to by weight. The resistance to aging is evaluated by determining the As compounds which are suitable for cationic copomodification of some mechanical properties of standard lymerization with formaldehyde or cyclic oligomers of 15 testing rods after storage for 1 year at 100 C. in a drying formaldehyde, preferably trioxane, there may especially cabinet. be used cyclic ethers and/ or cyclic acetals and/or linear The molding compositions in accordance with the prespolyacetals. Especially suitable are cyclic ethers having ent invention can be worked in the thermoplastic range from 3 to 5 ring members, preferably epoxides, furtherby injecction-molding, extrusion, blow molding, melt spinmore cyclic acetals having from 5 to 11, preferably from ning or deep drawing; they are suitable for the manufac- 5 to 8 ring members, and, more especially cyclic formals ture of semi-finished and finished articles, such as molded of ot,w-diols having from 2 to 8, preferably from 2 to 4 articles, for example ribbons, rods, bristles, threads, fibers, carbon atoms in the chain, the carbon chain of which plates, films, sheets, tubes or hoses, as well as houseware, may be interrupted by an oxygen atom at intervals of 2 for example, bowl or cups, and machine parts, for examcarbon atoms, as well as linear polyformals. ple, casings or gear wheels.

Especially suitable are compounds of the formula The following examples illustrate the invention; parts CHQ (CHR) IO (GH2) 1P0 and percentages being by weight unless otherwise stated.

in which R represents a hydrogen atom, an alkyl radical EXAMPLES 1 To 10 having from 1 t0 6, preferably from 1 to 3 carbon atoms, A copolymer made from 98% of trioxan and 2% of w i y be substituted y 1 to 3 halogen t p p ethylene oxide (RSV-value: 0.82 dl./g.) is mixed thorerably chlorine an alkoxymethyl radlcal havme oughly with 0.1% of calcium ricinoleate and the amounts from 2 to 6, preferably from 2 to 4 carbon at m a of stabilizer indicated in Table 1, and then granulated in P y radical a p y l y fadlcfill; x Stfll1dS a commercial extruder. The loss of weight is determined an integer of from 1 to 3, y bemg p 1n the 0r with the dried granules after their heating in air at 230 y is an integer of from 1 t0 1: being zero n 2 eing C. for 45 and 120 minutes, respectively.

2; or z represents an integer of from 3m 6, prefer ly 3 Furthermore, before and after heating for 30 minutes or 4, x be g Ze o and y belflg 1 111 fi 0386; to 230 C. in a closed mold, round compressed plates As cyclic ethers, for example ethylene crude and emhaving a thickness of 2.5 mm. and a diameter of 4.5 cm.

chlorhy y be used, a Well as P py OXlde, are prepared from the granules, and then the yellow styrene xid cyclohexene oxide, oxacyclobutane, p y coloration of the plates is determined. Table 1 shows that glycidyl ether and butanediol-diglycidyl ether, while as the stabilizer combinations used in accordance with the cyclic formals for example 1,3-di0xolane, 1,3-di xepane present invention are far superior to the stabilizers hitherand 1,3,6-trioxocane as well as 4-chloromethyl 1,3 dito used (see comparative Examples A to D) and that the oxolane, 1,3-dioxonane and 1,3 dl0xacycloheptene-(5) samples made from the molding compositions of the inare used. vention show considerably lower yellow values than the The polyoxymethylenes used in accordance with the comparative samples.

TABLE 1 Loss of weight, Yellow valuepercent at- Amount, After percent 45 120 30 Example Stabilizer by weight min. min. Before min.

A 1-[ ,'y-bis(4-hydroxy-3-sec.butyl-phenyl)-buturyloxy]d0decane 0.5 2.9 24 10.6 82.3 B do 1. o 1. 3 9 14. 3 s2. 5 C 1-[ -bls(4-hydroxy-3-sec.buty1pheny1)-butury1oxy]-ethane 0.5 2.9 17.2 7.5 81.3 D do 1.0 1.9 10.5 12.7 82.4

1 1,6-b1sIfi-(3,E-di-tert.-butyl-4-hydroxy-pheny1)-proplonyloxy]-hexane. 0.3 1.5 4.7 1.4 30.8 2 do 0.4 1.0 3.4 1.6 22.4 1 00 0.5 0.8 2.8 1.1 17.1 4 d0 0. 7 0. 5 2. 0 1. 7 15.2 5 1,1,l-tris[fl-(3,fi-di-tert.-butyl-4-hydroxypheny1)-propionyloxymethyl]-ethane -1 0.5 1.1 3.3 0.4 13.5 e do 0. 7 0. 9 2.8 1.4 20. 7 7 do 1. 0 0.83 2. 5 1.4 18.6 8 Tetrakislfi-(3,5-d1-tert.-butyl-4-hydroxy-phenyl)-pr0piony1oxymethyl]methane 0.5 0.74 5.4 1.5 16.3 a do 0.7 0. 5a 3.9 2.3 17.2 10 en 1.0 0.59 3.0 1.6 12.0

' EXAMPLES 11 TO 14 An acetylated formaldehyde homopolymer (RSV value: 0.85 dl./g.) is thoroughly mixed with 0.1% of calcium 7 stearate and the compounds indicated in Table 2 in an impeller mixer (abt. 1500 r.p.m.), and then granulated. After the granulation, the loss of weight of the samples is determined after heating in air at 230 C. for 45 and 120 minutes, respectively. Table 2 shows that the etfect of the stabilizer combination used in accordance with the 3,743,614 6 invention is far superior to that of the known stabilizers vention are processed (see Example no fur-like de- (see comparative Examples E and F). posit on.the wall of the equipment can be observed, while Furthermore, the granules are heated for minutes in in colpparatlve Example K the equlpment exhlbfts a F 'Y a closed mold, and round compressed plates having a dfiposlt after 70 a been Processed- In thls ful'lmg, thickness of 2.5 mm. and a diameter of 4.5 cm. are manu- 5 blsphenol as well as Imogen can be detected- Furthermore, the loss of weight of all three samples factured from the granules Subsequently the dlscolora after 120 minutes at 230 C. in air and the yellow coloration of the plates caused by the molding is determined. tion after 14 days of Storage in water at C. are

The Samples of the moldingcompositions of inven' termined. Although the same phenol radical is present in U011 Show substantlally lvOWel' yellow Values than the 10 all three phenol-alkanoic acid esters, there is a substanparative samples. tial ditference with respect to the effect. The mixture used TABLE 2 Loss of weight, Amount, percent after- Yellow percent value by 4 5 120 aft r Example Stabilizer A weight min. min. 30 min.

E Bis-[3-(Z-methylcyclohexyl)-5-methyl-2-hydroxyphe yl]-methane 0.5 1.1 35.0 20,2 F do 1.0 0.8 6.2 33. 2

11 TetrakisLB-(3,5,-di-tert.butyl-4hydroxyphenyl)-propionyloxymethyl]-methane 0.5 0.64 7.3 14.3 12 (in 1.0 0.54 4.2 12.3 13 1,2-bis['y-(3-tert.butyl-4-hydroxyphenyl)-pentanoy1oxy propane. 1. 0 0. 75 5. 7 15. 0 14 1. 0 0. 68 5. 2 16.2

1,4-bis(3-n1ethyl-5-tert.-butyl-4-hydroxy benzoyloxy)-butane..

in accordance with the invention shows the least dis- 25 coloration at storage in water and the least loss of weight.

TABLE 4 Yellow value Amount, Loss of percent by weight, After Example Stabilizer combination weight percent Before 14 days 1-(3,5-di-t rt.-buty1-4=hydroxy-benzoyloxy) n-octadecane 0. 5 K E i c ifi"f-i'n a1 h 1) 1 1 ma 3'2 1.3 3H

er u y y oXy-p eny -propiony oxy-n-oc ecane. L "{Calciumhydroxide 0.1

1, fi-bisfifi-(3,5-di-tert.-butyl-4-hydroxy phenyl)-propionyloxy]-hexane 0. 5 2o "{Oalcium hydroxide. 0.1

EXAMPLES 15 TO 19 7 EXAMPLE 21 A copolymer made from 96% of trioxan and 4% of A copolymer made from 98% of trioxan and 2% of 1,3-dioxolane (RSV value: 0.89 dl./g.) is thoroughly ethylene oxide (RSV value: 0.85 dL/g.) is mixed mixed with the stabilizer combinations indicated in Table thoroughly .with the stabilizer combinations indicated in 3, and granulated in a commercial extruder. After the Table 5,- and granulated in a commercial extruder. From granulation, the loss 'of weight of the samples'is deterthe granules, rods for the tensile strength test and plates mined after heating in air at 230 C. for 120 minutes. havinga dimension of 70 x 70 x 4 mm. are manufactured Table 3 shows the stabilizer combinations used in acinv an injection-extrusion molding machine. From the cordance with: the invention are by far superior to known plates, the standard rods required for the impact strength stabilizers (see comparative Examples G and I). I and impact strength notched tests are manufactured and TABLE 3 Amount, Loss of percent weight, Example Stabilizer combination by weight percent G {Bis[3-(2methyl-cyclohexyl)-5-methy1-2-hydroxy-phenyll-methane 0.5

Calcium stearate.-- 0.1 H Bis[3 (2-methyl-cyclohexyl)-5-methyl-2-hydroxy-phenyl]-methane 0.7 8 6 Calcium ricinoleate 0.1 I {4,4-bis(2-hydroxy-3-tert.butyl-6-methyl-pheny1)-h m1 0.7 7 3 Magnesium hydr -0. 1

15 {1,(rbis[fi-(3,5-di-tert. utyl-4-hydroxy-phenyl)-propionyloxy]-hexane 0.5 2 4 Magnesium hydr I I I l 0.1 16 {1,1,1-trisE:(3,5-di-tert-butyl-4-hydroxy phenyl)-propmnyloxymethyH-ethane..-- 0.5 3 7 Barium ydroxide--- 0.1 17 {Tetrakis[fl-(3,S-di-tert.butyl-t-hydroxy-phenyl)-propionyloxymethyl1-methane 0.5 3 2 Strontium hydr 0. 1 1 Tetrakis[6-(3,5-di-tert.butyl-4-hydroxy-phenyl)-propionyloxymethyl]-methane; 0.7 4 0 8 Calcium stearate j -0 2. 19 Tetrakis[B-(3,fi-di-tert.butyl 4-hydroxy-pheny1)-propionylcxymethyl]-Inethane 0.7 3 8 Calcium hydr 0.03

EXAMPLE 20 these rods are stored together with the rods for the tensile stren th test fo 200 kg. each of a copolymer made from 98 parts of trig r 1 yaar m a drymg oven at 100 oxan and 2 parts f ethylene oxlde (RSV value. 033 The values measured before and after the heat load are dL/g.) are stabilized by means of the stabilizer combinalisted in Table 5, and they show the superiorty of the dolls indicated in Table After granulation f drying, stabilizers used in accordance with the present invention the samples, one after the other, are processed into molded over a known Phmol (See comparative Example M). articles 1n an IHJCCtlOIl-CXU'USIOH molding machine. The Th temperature of the melt during this operation is 200 C., B tensile: Strength 13 measured accordmg to DIN the temperature of the equipment C. After the whole 45,455, the Impact Strength and the impact Strength 200 kg. of the molding composition according to the in- 7 notched according to DIN 53,453.

TABLE ts Impact strength Tensile strength notched (kpJcmJ) (kp.cm./cm. Amount, Impact strength (kp.cm./cm.=) percent by After After Example Stabilizer combination weight Before 1 year Before After 1 year Before 1 year Bis (-methyl-3-tert-.butyl-2-hydroxy-phenyl)- 0. 5 M methane. 620 413 Without break-- 16--. 6.4 1.0 Calcium ricinoleate 0. 1

TetrakisDS- (3,5-di-tert.-butyl-4-hydroxy-phenyl)- 0. 5 21.... propionyloxymethyH-methane. 630 628 .....do Without break... 6.6 5.5

Calcium ricinoleate 0. 1

EXAMPLE 22 TO 24 taining as polyoxymethylenes copolymers made from tri- A copolymer made from 98% of trioxam and 2% of oxan and cyclic ethers and/or cyclic acetals and/0r linear lyacetalst ethylene oxide (RSV value: 0.82 dl./g.) is thoroughly p0 mixed with the stabilizers listed in Table 6, and granulated Moldmg composltlons as clalmed m clam 1 in a commercial extruden The loss of weight of the taining as polyoxymethylenes copolymers made from triples of dried granules is determined after heating in air oxan and ff' cychc f' at f 45 and 120 minutes respectively 4 Molding composltions as claimed 1n claim 1 con- The synergistic eifect of the stabilizer combinations tammg as component (a) estersffi used in accordance with the invention, compared with the methylolethane Pentacrythr tol With -fi'( i eficct of various hydroxyphenyl-alkanoic acid compounds yq yp y )P p acldwithout addition of an alkaline earth metal compound M l g compositions a claimed 1n claim (see comparative Examples N to P) is shown in Table 6. taining as component (b) calcium salts of saturated or TABLE 6 Loss of weight, Amount, (percent) afterpercent by Example Stabilizer or stabilizer combination weight 45 min. 120 min.

N..-.- 1,1,l-tris[B-(3,5-di-tert.-butyl-4-hydroxy-phenyl)-propionyloxymethyl]-ethane.-..;-. 1.0 21 58 0--.. 1,6-bisLB-(3,E-di-tert.-butyl-4-hydroxy-phenyl)-propionyloxy]-hexane 1.0 17 68 P--.. TetrakisIB-(3,5-di-tert.-bnty1-4-hydroxy-phenyl)-propionyloxymethyl]-methane 1.0 19 41 22.... .{digtlrguggiggigtgra-butyl-4-hydroxy-phenyl)-propionyloxymethyl]-ethene 1 016 2A 23 --{1,6-bisb6-(of,5-di-tert.-butyl-4-hydroxy-phenyl)-propionyloxy]-hexane 1.0 o 55 1 8 Calcium r1cino1eate 0.1 24...;.-..;...{ggitgigfiggifigggggfirbutyl-4-hydroxy-phenyl)-propiony1oxymethyH-methane (159 What is claimed is: unsaturated aliphatic carboxylic acids having from 12 to 1. Stabilized polyoxymethylene molding compositions 40 18 carbon atoms. having incorporated therein a stabilizer composition con- 6. Molding compositions as claimed in claim 1 consisting essentially of v taining as component (b) calcium ricinoleate.

(a) from 0.05 to 4 percent by weight, calculated on p I the polyoxymethylene, of components of the formula References cltcll a. I I UNITED STATES PATENTS 3,206,431 9/1965 Doyle et a1. 260- 4185 H0 EM- 7 V p 3,484,400 12/1969 Halek 260--18 3,484,399 12/1969 Kakos 260-18 (A) 3,635,882 1/1972 Starretal. 260-457 in which R isan alkyl radical having from 1 to 6 C31- 3,644,482 2/1972 Dexter 26945-85 bon atoms, R is a hydrogen atom or an alkyl radical 3340219 9/1967 Stemmler 260-48 having from 1 .to 6 carbon atoms, A is a bito hexa- FOREIGN PATENTS valent aliphatic hydrocarbon radical having from 1 1 48 414 F 0 to 12 carbon atoms, m is zero or an integer of from 7/1967 rance 26 1 to 6 and n corresponds to the valence of A, and DONALD CZAJA, Examiner (b) from 0.01 to 3 percent by weight, calculated on the polyoxymethylene, of alkaline earth metal salts of RZUCIDLO Asslstant Examiner carboxylic acids having from 10 to 20 carbon atoms 7 U S X R and/or alkaline earth metal hydroxides.

2. Molding compositions as claimed in claim 1, con-, 260-457 R, 45.85 S, 45.95 

